1. Field of the Invention
The invention relates to an exhaust gas recirculation device of an internal combustion engine which includes a low-pressure EGR passage that connects an exhaust passage and an intake passage, and an high-pressure EGR passage that connects the exhaust passage upstream of the position of its connection with the low-pressure EGR passage and the intake passage downstream of the position of its connection with the low-pressure EGR passage, and a control method for the exhaust gas recirculation device.
2. Description of the Related Art
There is a known internal combustion engine which includes: a low-pressure exhaust gas recirculation passage that links an exhaust passage downstream of the turbine of a turbocharger and an intake passage upstream of the compressor of the turbocharger; a high-pressure exhaust gas recirculation passage that links the exhaust passage upstream of the turbine and the intake passage downstream of the compressor; a first recirculated exhaust gas control valve capable of controlling the amount of recirculated exhaust gas that flows in the low-pressure exhaust gas recirculation passage; and a second recirculated exhaust gas control valve capable of controlling the amount of recirculated exhaust gas that flows in the high-pressure exhaust gas recirculation passage, and in which the amount of exhaust gas that flows in the low-pressure exhaust gas recirculation passage and the amount of exhaust gas that flows in the high-pressure exhaust gas recirculation passage are controlled on the basis of the requested engine load (see Japanese Patent Application Publication No. 2005-076456 (JP-A-2005-076456)). There also is a known control device of an engine which includes a primary EGR passage and a secondary EGR passage that each connect an exhaust passage and an intake passage, and which controls EGR valves provided in the two EGR passages, respectively, so that the amount of flow of EGR gas that achieves a target EGR rate set from the engine load and the engine rotation speed is recirculated via the EGR passages (see Japanese Patent Application Publication No. 2000-130265 (JP-A-2000-130265)). Furthermore, there is a known internal combustion engine in which an exhaust passage or both the exhaust passage and an intake passage are provided with an oxygen concentration sensor or oxygen concentration sensors, and in which the amount of flow of EGR gas that is actually recirculated is found on the basis of the detected values from the one or more oxygen concentration sensors (see Japanese Patent Application Publication No. 08-121261 (JP-A-08-121261), and Japanese Patent Application Publication No. 10-141147 (JP-A-10-141147)).
The control device of Japanese Patent Application Publication No. 2000-130265 (JP-A-2000-130265) controls the degree of opening of each EGR valve on the basis of the operation state of the engine, that is, by a so-called open-loop control. As for the EGR valves, however, the correspondence relation between the degree of opening thereof and the amount of flow of gas passing therethrough changes due to time-dependent or aging changes, product variations, etc. Therefore, there is possibility of a targeted flow amount of EGR gas not being recirculated to the intake passage. In such a case, it becomes necessary to find the flow amounts of EGR gas actually recirculated to the intake passage via the EGR passages, and, on the basis of the recirculated flow amounts of the EGR gas, correct the correspondence relation between the opening degrees of the EGR valves and the passage flow amounts or correct the opening degrees of the EGR valves so that the targeted flow amount of EGR gas is recirculated. The actual EGR gas flow amount can be found on the basis of the detected values from the oxygen concentration sensors as described in Japanese Patent Application Publication No. 08-121261 (JP-A-08-121261) or Japanese Patent Application Publication No. 10-141147 (JP-A-10-141147). However, the technology described in either publication is a method applied to an internal combustion engine that has only one EGR passage, and no consideration is given to the application of the method to an internal combustion engine that has a plurality of EGR passages. If each EGR passage is provided with a sensor to detect the EGR gas flow amount, the cost increases.